For the industrial use of carbohydrates two principle possibilities were examined: The reduction of functionality by dehydration, like the synthesis of 5-hydroxymethylfurfural (HMF) or 5-glucosyloxymethylfurfural (GMF), leads to universal technical intermediates. In this work the potential of subcritical and supercritical water (SCW) as solvent and reaction media for the dehydration of D-fructose has been explored. The maximum selectivity regarding HMF of 30 % has been reached at 280 °C, 25 MPa and a residence time of 30 s. Under these conditions the activation energy was found to be 96 kJ/mol. A clear increase of selectivity could be obtained by addition of acetic acid as catalyst. Furthermore the influence of added salts has been examined. The addition of 400 ppm zinc sulfate results in the formation of lactic acid with a selectivity of 41 %. Carbohydrates can alternatively be refined under widely receipt of their structure and thus the natural synthesis performance to specialized end products, like carbohydrate carboxylic acids. Besides the synthesis via oxidation in SCW, the separation of the acids from aqueous solutions by reactive extraction has been investigated intensively. By use of the synergistic extractant system consisting of 1-butanol and tri-n-octylamine (TOA) D-gluconic acid can be extracted with a distribution coefficient of 3.5. The influence of different parameters like temperature, amine/acid-ratio and additions of glucose as well as electrolytes was examined. The mass transfer coefficient of the acid extraction has been determined by experiments on individual drops. Based on these insights a concept for a technical process is proposed. Furthermore the extractant system 1-butanol/TOA is suitable for the separation of glucose oxygenates like glucaric, gluconic and glucuronic acid for which a technical process is also suggested.